1. Field of the Invention
The present invention relates to a vehicular headlamp and more particularly to a vehicular headlamp that includes a beam radiation unit rotatably installed inside a lamp body.
2. Prior Art
One of known headlamps for vehicles, for example automobile headlamps, includes a beam radiation unit that has a discharge bulb as its light source and is rotatably supported inside the lamp body. In this headlamp, the beam radiation unit is rotated in the steering direction in accordance with, for instance, the steering operations so that the front of the vehicle is illuminated more intensely.
For the discharge bulb to be lit, it is necessary to apply high DC illumination voltage. For this purpose, an illumination circuit that includes a ballast circuit and an actuation circuit (starter circuit) are required in which the ballast circuit is formed with a DC-DC pressure increase circuit that increases the voltage from a DC power source and with a DC-AC switch circuit that converts the thus increased DC voltage to AC voltage (illumination voltage), and the actuation circuit (starter circuit) applies voltage which is necessary to actuate the discharge bulb (starting discharging) to the illumination voltage.
In this structure, the illumination circuit and the discharge bulb are connected via a cord. The illumination circuit is generally not a small circuit size-wise that can be connected directly to a connector of the discharge bulb; rather it occupies a large space and has a significant weight when the illumination circuit is formed as an illumination circuit unit that is housed inside a metallic case in view of the electromagnetic shield and heat released from heat-generating parts, etc.
Because of these situations, the illumination circuit is mounted on the lamp body, and the illumination circuit unit and the discharge bulb are connected via a cord.
In this case, if the beam radiation unit is installed so as to be rotated freely, several problems occur. The cord deforms and moves around every time the beam radiation unit is rotated, thus contacting with other components inside the lamp body and getting damaged. In addition, the cord is caught by other members, and the rotation of the beam radiation unit is hindered. Furthermore, the beam radiation unit cannot rotate as expected if a portion of the cord that is deformed or moved upon rotation of the beam radiation unit is long and the cord becomes unable to deform freely when the cord is frozen at low temperatures, making the rotation of the beam radiation unit difficult.